Patients with well-documented post-transfusion chronic non-A, non-B (non-lupoid) hepatitis are being evaluated to determine the natural history of this disease and to obtain tissues and reagents to search for non-A, non-B agents. Thirty patients have been admitted to this study. These patients have undergone thorough evaluations including a liver biopsy. They have had the disease for periods ranging from 1 to 11 years. Seven patients have a mild degree of malaise, the remaining patients are asymptomatic. Liver biopsies have revealed chronic persistent hepatitis in seven, chronic active hepatitis in twenty-one and alcoholic liver disease in two. Six patients have developed cirrhosis and one of these has dried of hepatocellular failure. Trials of immunosuppressive and antiviral therapy for these patients are being planned. A pilot study of Acyclovir therapy has been carried out in five patients. No consistent effect of the drug on aminotransferase levels was observed. A pilot study of recombinant human leukocyte interferon has been initiated.